"They have fruit"
Because you can use the personal pronoun anytime you want, but it is not necessery. It is used especially to emphasize who is doing the action.
E.g. both of "ninakula" and "mimi ninakula" mean "I am sleeping" or "I sleep" and both are correct. In the second case the "I" is emphasized.
In English it seems strange because you need to use the personal pronoun every time but in lot of languages it is not necessary because the conjugation of the verbs already shows you who is the subject (Italian, Hungarian, Slavic languages etc. - just like Martin633120 wrote it).
Thanks for referring to my comment which was meant as a reply to Valerie's question. In your comment, you of course didn't mean "I am sleeping" or "I sleep" as translations of "ninakula" and "mimi ninakula", but you know "mimi ninakula" and "ninakula" are two expressions for saying "I'm eating" or "I eat".
I think you find something similar in many languages--cases where it's arbitrary whether you use the personal pronoun or not when the grammatical form of the verb already tells you which person it is. Do you follow me? It's certainly true with Russian and the other Slavic languages anyway.
But fruit is not singular. The word itself is plural. Theres no way to make it a singular word. Even if you say "this apple is a fruit" fruit is referring to a whole genre. Even "this is a fruit"...fruit is still a classification that encompasses everything classified as a fruit. Interesting.....